The present invention relates to a method of and to an apparatus for forming and processing a stream of fibrous material, particularly a stream of natural, reconstituted and/or substitute tobacco which can be converted into the rod-like filler of a cigarette rod or the like. More particularly, the invention relates to improvements in a method of and in an apparatus for forming a stream which is obtained by accumulating fibrous material into successive increments of the stream, conveying such increments along an elongated path, monitoring the density of successive increments of the stream, and influencing one or more parameters which determine the characteristics of the stream as a function of fluctuations of the monitored density. A thus treated stream can be used for conversion into a constituent of a rod that is ready for subdivision into filter rod sections, plain cigarettes, cigarillos and like rod-shaped articles which constitute or form part of smokers' products. For the sake of simplicity, the following description of the invention and of conventional methods and apparatus will deal with a method and apparatus for the making of a stream which is converted into the filler of a cigarette rod with the understanding, however, that such method and apparatus can be resorted to with equal advantage for the making of streams which are ready for conversion into or which constitute rod-like fillers for other types of smokers' products or constituents of smokers' products.
Timely ascertainment of various characteristics of a tobacco stream is highly desirable and advantageous because this renders it possible to immediately or practically immediately undertake the necessary corrective measures when the quality of the finished product or of an intermediate product deviates from an optimum quality. For example, it is desirable and advantageous to ascertain the density of the tobacco stream which is about to be converted into or which already constitutes the filler of a cigarette rod. Timely detection of the distribution of density in the longitudinal direction of the tobacco stream ensures that the cigarette making machine will not turn out excessive numbers of cigarettes with soft ends which are conducive to escape of tobacco shreds with attendant contamination of the pocket, purse, table top, floor and/or the interior of the pack. Thus, timely detection of various characteristics, particularly density, of a tobacco stream renders it possible to achieve a great reduction in the number of rejects, customer complaints, distributor complaints and switches to different makes of cigarettes.
The results of the measurements of density of a tobacco stream are used with advantage for regulation of the make-up (composition) of the stream for a large number of years. In accordance with a presently known proposal, the density of the tobacco stream is monitored by a detector which employs a source of beta rays and a transducer in the form of an ionization chamber serving to generate electric signals which are indicative of the density of successive unit lengths of the stream. A drawback of such mode of measuring the density of a tobacco stream is that the measurement is not sufficiently accurate and that the inertia of the detector is high, primarily due to the characteristics of the ionization chamber. Moreover, such detectors are merely capable of generating signals which are indicative of the average density of the monitored stream, i.e., the signals are actually integrals of the densities in various cross-sectional areas of the stream. In other words, the just discussed conventional measurement of density cannot furnish any information regarding the distribution of density in various sections of the stream, such as at the center, close to the periphery or midway between the periphery and the center of the stream.
U.S. Pat. No. 3,056,026 to Bigelow discloses a cigarette density gage which utilizes a source of X-rays in conjunction with a dual ion chamber. The ion chamber is designed to transmit electric signals which are indicative of the average density of the stream, i.e., of an integral of density across the entire cross-section of the monitored portion of the stream. The gage of Bigelow also fails to furnish any information which could be used to ascertain the distribution of density in selected portions of a tobacco stream, as considered at right angles to the longitudinal axis of the stream. On the other hand, timely detection of density variations in various strata of the tobacco stream, in addition to or in lieu of detection of eventual fluctuations of density as considered in the longitudinal direction of the stream, could assist the manufacturer in carrying out adjustments which would greatly enhance the quality of the ultimate product, which would bring about pronounced savings in tobacco, which would reduce the number of rejects and/or which would reduce the number of down times for manual adjustments and/or repairs of the cigarette rod making machine and/or of machines which supply various starting materials to and/or receive rod-shaped articles from a cigarette maker.